The Acquired Immunodeficiency Syndrome (AIDS), a disorder of unknown etiology, is probably transmitted by blood, blood products or secretions. Most investigators believe that a microbial agent is responsible for the immunosuppression observed. Since blood is important in transmission, it is likely that the putative etiologic agent is present in the blood at some point in the natural history of the disorder. Based on the natural history of many other infectious diseases, not all those infected with an etiologic agent become ill. It is possible that there have been persons affected by the etiologic agent of AIDS who have recovered or who have subclinical infections. Some of these persons may have serum antibodies to the specific agent, antigenic components, or to host factors (such as cardiolipins). We plan to develop methods to detect antibody-antigen complexes involving the putative AIDS agent. Methods to be employed will include immunodiffusion, immunoelectrophoresis, counterimmunoelectrophoresis, and enzyme-line immunosorbent assays (ELISA). Populations to be screened include patients with AIDS, patients with the chronic lymphadenopathy syndrome, homosexuals and healthy heterosexual controls. For those serum combinations for which precipitation or binding appears to have taken place, we will fractionate the serum to determine whether the reaction is immunologically mediated. If the reaction is immunologically mediated, we will begin procedures to characterize the antigen. If the reaction is non-immunologic we will define the specificity to determine whether it still could be useful as a screening test for AIDS-carriers.